Alloa, bossed by former Rangers and Scotland skipper Barry Ferguson, will be massive favourites and Horn knows it will be a huge upset if his Lowland League leaders can overcome their cinch League 1 opponents.
But the New Dundas Park gaffer says Rose’s aim will be the same as it it would be for any other match – to win.
Horn said: “It's a massive test. We could have got easier ties, there's no doubt about that.
"Alloa were a Championship team last year and have got guys that have played in the Premier League in their squad.
"Their manager's played at a very high level as well so we're under no illusion show difficult a task it is.
"But at the same time we go there with no fear; it's a free hit.
"Obviously we respect our opponents and the level they're playing at. They're a good side.
"We go through there needing a bit of luck but if we play as well as we can you never know what can happen.
"They're not any different to any of the other teams we've played against. We played Dundee last year and it was the same kind of idea; we went about our business and knew that we'd have to defend at times and that we wouldn't have as much of the ball as we would normally have and I expect it to be exactly the same on Saturday.
"There will be times when we'll really have to defend and be organised, but when we've got the ball we've got to be good and create opportunities, and when we get opportunities we’ ve got to take them.
"It's a difficult task and in these games you need a bit of luck as well but we'll give it our best shot and see what happens. We're there to win the game, it's as simple as that.
"We're really looking forward to the game. Hopefully there's a big crowd there and a big Bonnyrigg following.
"The prices might put a few people off but I still think the Bonnyrigg fans will go through in their numbers."
Bonnyrigg warmed up for their game with a 4-0 South Region Challenge Cup win over Coldstream on Saturday – their 13th consecutive win in all competitions.